One important component of the host antiviral response is the type I IFN system. Type I IFN is synthesized in response to viral infection. Double stranded RNA (dsRNA) or viral infection activate latent transcription factors, including IRF-3 and NF-kB, resulting in transcriptional up-regulation of type I IFN, IFN-α, and IFN-β genes. Secreted type I IFNs signal through a common receptor, activating the JAK/STAT signaling pathway. This signaling stimulates transcription of IFN-sensitive genes, including a number of that encode antiviral proteins, and leads to the induction of an antiviral state. Among the antiviral proteins induced in response to type I IFN are dsRNA-dependent protein kinase R (PKR). 2′,5′-oligoadenylate synthetase (OSA), and the Mx proteins (Clemens et al., 1997 Interferon Cytokine Res. 17:503-524; Floyd-Smith et al., 1981 Science 212:1030-1032; Haller et al., 1998 Rev. Sci Tech 17:220-230; Stark et al., Annu Rev. Biochem 67:227-264).
Many viruses have evolved mechanisms to subvert the host IFN response. For example, the herpes simplex virus counteracts the PKR-mediated phosphorylation of translation initiation factor cIF-2α, preventing the establishment of an IFN-induced block in protein synthesis (Garcia-Sastre et al. 1998 Virology 252(2):324-30). In the negative-strand RNA viruses, several different anti-IFN mechanisms have been identified (Garcia-Sastre et al., 1998 Virology 252:324-330).
Citation of a reference in this section or any section of this application shall not be construed as an admission that such reference is prior art to the present invention.